I thought about this a bit last night. I think that the best height for the top of the barrel from the ground, with the rifle standing straight up, is the height at which the arc of my right arm allows me to insert and remove the ramrod and pack the charge without having to adjust my grip on my ramrod. Belt buckle level seems about the minimum height for the top of the barrel, while bottom of my ribcage seems about the max comfortable height. I am 6'1"+- an inch with a 36" inseam on jeans, so my perfect barrel height would vary some from people of different heights, much like the height of our perspective dream flatheaded, midget waitresses/servers/hookers.

The rifles carried by hunters on foot were long barreled. The rifle was not always fatal from the first shot. The hunters preferred a rifle that put the muzzle near the shooters nose. The idea being the gun could be loaded while the shooter watched his target.
The heavy barreled short Hawken type rifle referred to as a "Yeager" by Western hunters was designed for the horse back hunters of the open plains. The Hawken did not need the balance of a Long rifle. It was heavy barreled and thick wristed for dangerous Western game.
The art of speed loading any muzzle loader was to simply pour the powder don't measure and spit a naked ball down the bore. Men like Wetzel could and did load their flint locks on a dead run.

The rifles carried by hunters on foot were long barreled. The rifle was not always fatal from the first shot. The hunters preferred a rifle that put the muzzle near the shooters nose. The idea being the gun could be loaded while the shooter watched his target.
The heavy barreled short Hawken type rifle referred to as a "Yeager" by Western hunters was designed for the horse back hunters of the open plains. The Hawken did not need the balance of a Long rifle. It was heavy barreled and thick wristed for dangerous Western game.
The art of speed loading any muzzle loader was to simply pour the powder don't measure and spit a naked ball down the bore. Men like Wetzel could and did load their flint locks on a dead run.

The rifles were fired from rest the long barrel also aided resting on tree limbs etc. When inspecting originals you will often find the rear sight has moved forward and rear ward many times. This was done to compassionate for aging eyes. The longer barrel was also considered to be more efficient with black powder.
Many of these rifles had the barrels shortened as the hunters moved from the forest to the plains. The horse changed the long arms of the day.